Oath of the Kings of the Belgians

The swearing-in ceremony (Dutch: eedaflegging; French: prestation de serment) occurs when the Belgian heir-apparent or heir-presumptive takes the oath that allows him or her to become King or Queen regnant of the Belgians. Article 91 of the Belgian Constitution outlines this ceremony, which transpires no later then ten days after the death or abdication of the previous monarch, at the Palace of the Nation in Brussels, the seat of the Belgian Parliament. Should the monarch be unable to govern for more than ten days, the same oath is taken by the regent appointed by the Chambers.

A significant and symbolic act in the Belgian constitutional monarchy system, the swearing-in of the oath distinguishes itself from the automatic successions of Ancien Régime monarchies. It conditions the accession of the sovereign to the throne. By accepting their constitutional mandate, the monarch becomes the Nation's delegate and can exercise the prerogatives devolved to them by the Constitution.

The date of Leopold I's swearing-in (21 July 1831) is marked annually by Belgian National Day, a public holiday, established by law on 27 May 1890.